1. Field of the Invention
The subject invention relates to vehicle maintenance and, more particularly, to an apparatus for withdrawing and replenishing transmission fluid in an automatic transmission.
2. Description of the Prior Art
Automatic transmissions require transmission fluid because such fluid is employed to transmit torque within the transmission and is additionally employed to lubricate the internal components within such transmissions. Over time such fluid becomes less viscous and thus less efficient in lubricating such components. It is therefore desirable to periodically perform an exchange of fluid to maintain the viscosity of such fluid within the transmission and to maintain the cleanliness of the transmission and thereby increase the useful life of the transmission. A complete exchange of fluid is preferred so that the used fluid as well as undesirable foreign matter contained therein is completely removed and is replaced with new, more viscous fluid.
Automatic transmissions typically include transmission fluid filters which serve to aid in the removal of undesirable foreign matter from the transmission fluid. In most transmission systems the fluid filter is internally disposed within the transmission housing. However, certain transmission systems such as transmissions used in tractors sold under the trademark ALLISON incorporate external transmission fluid filters integrated into the transmission fluid cooler lines extending between the vehicle's transmission and the radiator. In addition, it has been known that in the coming years automobile manufacturers such as Ford, Chrysler, and General Motors will manufacture transmissions incorporating external transmission filters.
There has been a long standing need for a device which may efficiently perform a simultaneous, substantially complete exchange of transmission fluid in an automatic transmission while at the same time posing minimum risk to the transmission. The conventional method, still widely practiced today, is to replace the fluid housed in the pan of the transmission. The pan typically holds from 1 to 5 quarts of the total 7 to 15 quart capacity of the transmission. Thus emptying the pan and then adding that amount of new fluid only serves to dilute the used fluid with some 15%-25% of new fluid. Hence this conventional service is inefficient since it only serves to mix new fluid with a large quantity of used fluid. Furthermore, this service requires the removal of the transmission fluid pan from the transmission for emptying of the fluid therefrom and replacement of the pan on the transmission housing. This is a messy and time consuming process. Furthermore, the pan is often not replaced squarely over the pan seal or, on occasion, will trap small foreign obstacles in the seal area resulting in leakage.
More recently, there have been efforts to change all the fluid in an automobile's transmission by disconnecting a fluid tube and draining the fluid into a waste oil dump while manually pouring new fluid into the transmission dipstick hole. This procedure has proven to be inefficient, inadequate and so time consuming that it has failed to gain broad acceptance.
Another prior method involved disconnecting a transmission fluid cooler line and allowing one end of such cooler line carrying used fluid to drain freely, while the other end of the line was connected to a pressurized tank which injected unused fluid into the cooler line connected to the transmission. One major disadvantage associated with this method is that, in many instances, the rate at which fluid exits the transmission cannot be matched by the rate at which unused fluid is injected into the transmission because the transmission, due to internal resistances, cannot accept fluid at the same rate as the rate at which used fluid is flowed by the transmission pump into an unrestricted cooler line. As such, there is a risk that, because of unbalanced flow, the transmission pump may run short of fluid resulting in the fluid seals, rear bearings and other internal components of the transmission being exposed to damage due to the progressively diminishing level of fluid in the transmission during such a process. This difficulty is compounded by the fact that the flow resistance varies with the different models of transmissions.
Other work in this field has led to the proposal of a transmission changer including air pressurized tanks for supply and extraction of transmission fluid via the transmission cooling lines. A device of this type is shown in U.S. Pat. No. 5,318,080 to Viken issued on an application filed Oct. 25, 1991. This device suffers the shortcoming that it must be tied to an air pressure hose like an umbilical cord, is expense to manufacture and requires access to the vehicle transmission fluid plumbing lines.
In my prior U.S. Pat. No. 5,370,160, I disclose a transmission flushing device which breaks into the transmission cooling lines leading from the radiator. While providing an important solution to a long standing problem, that arrangement could be improved by providing an adaptor which would allow access to the flow stream from the transmission without the necessity of cutting into the cooling lines.
As such, it may be appreciated that there continues to be a need for an automatic transmission fluid exchanging device which provides convenient access to the transmission for simultaneous exchange of fluid, while at the same time posing minimum risk of damage to the transmission or tubing associated therewith. The instant invention addresses such needs.